''Allopetrolisthes spinifrons'' is a species of porcelain crab. It displays "hypercarcinisation", whereby the resemblance to a

true crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...

is enhanced by

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

of the abdomen. It lives along the Pacific coast of Peru and Chile, as a symbiont of a

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

Description

''Allopetrolisthes spinifrons'' grows to a maximum

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

length of around . It displays an extreme form of carcinisation –

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

of a crab-like form – referred to as "hypercarcinisation". In contrast to other porcelain crabs, ''A. spinifrons'' shows

of the pleon (abdomen), closely resembling the situation in true crabs. Females have a large pleon, similar to that of other porcelain crabs, covering almost all of the sternum. Males have a short, triangular pleon that only covers a small part of the sternum. ''A. spinifrons'' also differs from its relatives in having many fewer and smaller spines on its legs. These morphological differences are thought to be a consequence of the species' ecology, living in close association with a

, where the ability to escape by swimming is not needed.

Distribution and ecology

''Allopetrolisthes spinifrons'' is found in the eastern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

, from Isla San Lorenzo,

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

to San Vicente,

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

, at depths of up to . ''A. spinifrons'' lives symbiotically on the

'' Phymactis papillosa'', chiefly in the lower

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

. In common with other porcelain crabs, ''A. spinifrons'' is a

filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

, but will also feed on faeces and

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

produced by the sea anemone. The porcelain crab benefits from the protection afforded by the sea anemone's stinging cells.

Taxonomy

''Allopetrolisthes spinifrons'' was first described in 1837 by

Henri Milne-Edwards Henri Milne-Edwards (23 October 1800 – 29 July 1885) was an eminent French zoologist. Biography Henri Milne-Edwards was the 27th child of William Edwards, an English planter and colonel of the militia in Jamaica and Elisabeth Vaux, a Frenchw ...

, under the name ''Porcellana spinifrons''. It was placed in the genus ''

Petrolisthes ''Petrolisthes'' is a genus of marine porcelain crabs, containing these extant species: *'' Petrolisthes aegyptiacus'' Werding & Hiller, 2007 *'' Petrolisthes agassizii'' Faxon, 1893 *''Petrolisthes amoenus'' (Guérin-Méneville, 1855) *'' Pet ...

'' by

Giuseppe Nobili Giuseppe Nobili (1877-1908) was an Italian zoologist at the University of Turin, specialising in Crustacea, who was born at Omegna in Piedmont in 1877 and died at Omegna in 1908. His father was Dr. Gaudenzio Nobili and his mother, Adele Antonioli ...

in 1901, and moved to the new genus ''

Allopetrolisthes ''Allopetrolisthes'' is a genus of porcelain crabs, comprising three species: *'' Allopetrolisthes angulosus'' (Guérin, 1835) *''Allopetrolisthes punctatus ''Allopetrolisthes'' is a genus of porcelain crab Porcelain crabs are decapod ...

'' by Janet Haig in 1960, alongside two other species formerly placed in ''Petrolisthes''.

Description

Distribution and ecology

Taxonomy

References

Further reading